Learning the Metric System

Every country in the world uses the metric system except Liberia, Burma and the U.S. If you travel outside the U.S. you will have to deal with the metric system. Within the U.S. there are some areas that use the metric system (also International System of Units or simply SI). This is why learning the metric system is so important. You buy a 2-liter bottle of soda. Medicine is measured in grams or milliliter (ml). The SI prefixes are used in computers. Food labels show quantities in grams. Most science is done using SI units.

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In school, you are taught the units for mass, length, volume and time. Mass (often incorrectly referred to as weight) is grams, length is meter, volume is liter and time is second.

What are the prefixes?

When learning the metric system the prefixes are a standard set of words that indicate the size of the unit. So, for instance, a kilometer means 1000 meters. The prefixes are used with all of the standard units in the same way. A kilogram is 1000 grams and a kiloliter is 1000 liters. In school, students are taught six basic prefixes; kilo, hecto, deka, deci, centi and milli.

Kilo = 1000Hecto = 100Deka = 10Deci = 1/10Centi = 1/100Milli = 1/1000

There are actually 20 defined prefixes, but this article focuses on the ones taught in school.

How to convert metric units

When learning the metric system there is a popular mnemonic used for learning these six prefixes.

King Henry Died By Drinking Chocolate Milk.

The word ‘By’ refers to the base unit such as meter, liter, or gram.

By learning this easy mnemonic, you can learn the six basic prefixes and their order. Knowing the order will help you perform metric conversions, such as from centimeters to meters. This is how it works.

How many meters in 1523 centimeters?

Using the mnemonic, write the first letter of each word. K H D B D C M.

Find the “C” for centimeters then find the “B” for base unit. It is two letters to the left. Now move the decimal point the same number of places and in the same direction, that is, move the decimal point two places to the left. So 1523 become 15.23.

1523 centimeters becomes 15.23 meters!

Let’s go the other direction. How many millimeters are in .00298 hectometers?

Starting with the “H” for hecto, move to the “M” for millimeter. You move five places to the right.

.00298 hectometers becomes 298 millimeters.

Sometimes you may have to add zeros in front or behind the number to be able to move the decimal point enough places. As in the previous example, if you went from 298 millimeters to hectometers, you have to add two zeros in front of 298 so that you can move the decimal five places to the left.